An expansion anchor is known, for example, from DE 4116149 A1. It is used for anchoring mounting parts to a borehole in a fixed substrate, for example, a concrete substrate. The known expansion anchor has an elongated bolt, which is provided with an expansion cone in the area of its front end, and which has a thread in the area of its rear end, on which a nut is seated. The expansion cone expands toward the front end, i.e., against the extraction direction. In the extraction direction, an expansion sleeve is situated on the bolt offset to the expansion cone. Toward the front end of the bolt on the expansion cone, this expansion sleeve is displaceably mounted on the bolt. Toward the rear end of the bolt, the displacement of the expansion sleeve in relation to the bolt is delimited by a stop formed as an annular shoulder.
When setting the anchor, the first end of the bolt is pounded into the borehole in the substrate against the extraction direction. The expansion sleeve is entrained by the annular shoulder and therefore also reaches the borehole. The nut is then screwed on until it stops on the substrate or a mounting part, which may be present as an abutment, and it is then tightened further until a predefined torque is reached. This tightening of the nut causes the bolt to be pulled back out of the borehole to a certain extent in the extraction direction. After the expansion anchor is pounded in, the expansion sleeve is caught on the inner borehole wall and is therefore retained upon withdrawal of the bolt in the borehole. As a result, the expansion cone of the bolt is drawn into the expansion sleeve, the expansion sleeve being expanded due to the increasing diameter of the expansion cone. The expansion anchor is jammed with the expansion sleeve in the substrate, so that tensile loads may be transferred into the substrate. This basic principle may preferably also be used in the anchor according to the present invention.
When expansion anchors are used under actual surrounding conditions, sand or drill cuttings may possibly reach the thread of the bolt, which may result in an undesirable increase of the friction between nut and bolt, and thus an increase of the required torque for tightening the nut. In extreme cases, the friction of the nut on the thread may exceed the friction of the bolt in the expansion sleeve. In this case, an undesirable jamming between nut and bolt may occur. The bolt then slips in the sleeve so that the nut may not be screwed on and the anchor may not be set easily.
To prevent such slippage, i.e., to prevent such undesirable rotation of the bolt in relation to the sleeve, the most proximate U.S. Pat. No. 3,855,896 A proposes the provision of a knurling on the circumference of the bolt, starting from the annular shoulder, which acts against the expansion sleeve from within, and increases the friction between the bolt and sleeve.
DE 2256822 A1 also concerns anti-twist devices of the expansion sleeve on the bolt. In contrast to U.S. Pat. No. 3,855,896A, in which the anti-twist device is implemented by increased friction, DE 2256822 A1 proposes anti-twist devices by appropriate geometric shapes, i.e., form-locked anti-twist devices.
Additional expansion anchors having anti-twist devices between the expansion sleeve and bolt are described in DE 29501182 U1, DE 3411285 A1, GB 1414562 A, CA 953958 A1, DE 2161224 A1, U.S. Pat. No. 3,750,526 A, EP 0 874 167 B1 and DE 6610690 U.
According to EP 0893610 A1, an anti-twist protection of the bolt is implemented by webs projecting radially from the bolt, the webs acting directly against the borehole wall.
DE 10 2008 057 584 A1 describes an expansion anchor, in the neck area of which at least three reinforcing ribs are situated, which extend to the stop shoulder, and which are intended to be used for releasing tensions, in particular in the case of transverse stress.
According to DE 3508015 A1, the stop area located perpendicular to the longitudinal axis of the bolt and formed on the shoulder for the sleeve merges via a concave fillet into the lateral surface of the cylindrical neck area of the bolt, which is intended to avoid the occurrence of a sharp edge having a tendency to break.